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Chapter 15 Plate Tectonics
Section 1 Inside the Earth
Section 2 Restless Continents
Section 3 The Theory of Plate Tectonics
Section 4 Deforming the Earth’s Crust
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Concept Mapping
Chapter 15 Section 1 Inside the Earth
Question of the Day
If you journeyed to the center of the Earth, what doyou think you would see along the way?
Draw an illustration of the journey for your QOD.
Chapter 15
Objectives
• Identify the layers of the Earth by their chemical composition.
• Identify the layers of the Earth by their physical properties.
• Describe a tectonic plate.
• Explain how scientists know about the structure of Earth’s interior.
Section 1 Inside the Earth
Chapter 15
The Composition of the Earth• The Earth is divided into three layers.•Crust •Mantle•Core
• Crust - the thin and solid outermost layer of the Earth above the mantle.
•Crust is 5 to 100 km thick, and is the thinnest layer of the Earth.
Section 1 Inside the Earth
Chapter 15
The Composition of the Earth, continued• Two types of crust—continental (land) and oceanic (ocean).•Oceanic crust is thinner and denser than continental crust.
Section 1 Inside the Earth
Chapter 15
The Composition of the Earth, continued• Mantle - the layer of rock between the Earth’s crust and core.
•The mantle is much thicker than the crust, it makes up about 2/3 of Earth.
• We have never dug down that deep, so scientists must draw conclusions about what the mantle is made of and other physical properties from the Earth’s surface.
Section 1 Inside the Earth
Chapter 15
•Core - the central part of the Earth below the mantle.
•The core makes up about one-third of Earth’s mass.
• Scientists think that the Earth’s core is made mostly of iron.
Section 1 Inside the Earth
The Composition of the Earth, continued
Chapter 15 Section 1 Inside the Earth
Chapter 15
The Physical Structure of the EarthThe Earth is divided into five physical layers:
1. The lithosphere2. The asthenosphere3. The mesosphere4. The outer core5. The inner core
Each layer has its own set of physical properties.
Section 1 Inside the Earth
Chapter 15
Physical Structure of the Earth, continued• Lithosphere – the solid, outer layer of the Earth that consists of the crust and the rigid upper part of the mantle.
• The lithosphere is divided into pieces that are called tectonic plates.
Section 1 Inside the Earth
Chapter 15
• Asthenosphere - the soft layer of the mantle on which the tectonic plates move.
• The asthenosphere is made of solid rock that flows very slowly.
Section 1 Inside the Earth
Physical Structure of the Earth, continued
Chapter 15 Section 1 Inside the Earth
Chapter 15
• Mesosphere - is the strong, lower part of the mantle between the asthenosphere and the outer core.
• The prefix meso- means “middle.”
Section 1 Inside the Earth
Physical Structure of the Earth, continued
Chapter 15
• Earth’s core is divided into two parts.
• The outer core is liquid and is right under the mantle.
• The inner core is solid iron and is the center of the Earth.
Section 1 Inside the Earth
Physical Structure of the Earth, continued
Chapter 15 Section 1 Inside the Earth
Chapter 15
Tectonic Plates• Tectonic Plate – a block of lithosphere that consists of the crust and the rigid, outermost part of the mantle.
• These plates make the Earth look covered in puzzle pieces.
Section 1 Inside the Earth
Chapter 15
Tectonic Plates, continued• A Giant Jigsaw Puzzle Each tectonic plate fits together with the tectonic plates that surround it.
• The lithosphere is like a jigsaw puzzle. The tectonic plates are like the pieces of the puzzle.
Section 1 Inside the Earth
Chapter 15
Tectonic Plates, continued• A Tectonic Plate Close-Up The following Visual Concept presentation shows the Earth’s major tectonic plates and how they fit together.
• The presentation also illustrates what a tectonic plate might look like if you could lift it out of its place.
Section 1 Inside the Earth
Chapter 15
Tectonic Plates, continued• Tectonic plates “float” on the asthenosphere.
•The plates bump into one another when they move.
Section 1 Inside the Earth
Chapter 15
Mapping the Earth’s Interior•Since we can’t dig in the Earth how do we know what is there? •Scientists measure speeds of seismic waves that travel through the Earth’s interior during earthquakes.
• By using seismographs, scientists have learned that the Earth is made of different layers.
Section 1 Inside the Earth
Chapter 15 Section 2 Restless Continents
Question of the Day
What is meant by the following statement:“The United States is moving westward.”
From what you know about geology and plate tectonics explain if you believe this statement to be true or false.
Chapter 15
Objectives
• Describe Wegener’s hypothesis of continental drift.
• Explain how sea-floor spreading provides a way for continents to move.
• Describe how new oceanic lithosphere forms at mid-ocean ridges.
• Explain how magnetic reversals provide evidence for sea-floor spreading.
Section 2 Restless Continents
Chapter 15
Continental Drift Hypothesis
• Continental drift - the hypothesis that states that continents once formed a single landmass, broke up, and drifted to their present locations.
Section 2 Restless Continents
Chapter 15
The Breakup of Pangaea• It was theorized that all of the present continents were once joined in a single, huge continent he called Pangaea.
• Pangaea is Greek for “all earth.”
• Pangaea existed about 245 million years ago.
Section 2 Restless Continents
Chapter 15
Sea-Floor Spreading• Evidence supporting continental drift hypothesis comes from sea-floor spreading.
• Sea-floor spreading - the process by which new oceanic lithosphere forms as magma rises toward the surface and solidifies.
Section 2 Restless Continents
Chapter 15
Sea-Floor Spreading, continued•Mid-ocean ridges are underwater mountain chains that run through Earth’s ocean basins where sea-floor spreading takes place.
Section 2 Restless Continents
Chapter 15 Section 2 Restless Continents
Chapter 15
Sea-Floor Spreading, continued•Some of the most important evidence of sea-floor spreading comes from magnetic reversals recorded in the ocean floor.
•Molten rock at the mid-ocean ridge contains tiny grains of magnetic minerals that act like compasses.
Section 2 Restless Continents
Chapter 15
Sea-Floor Spreading, continued• When the Earth’s magnetic field reverses, the magnetic mineral grains align in the opposite direction. The new rock records the direction of the Earth’s magnetic field.
Section 2 Restless Continents
Chapter 15 Section 3 The Theory of Plate Tectonics
Question of the Day
If the sea floor is spreading an average of 4 cm ayear, how many years did it take New York and the west coast of Africa to reach their current locations, 6,760 km apart?
Calculate your answer in your science journal.
Chapter 15
Objectives
• Describe the three types of tectonic plate boundaries.
• Describe the three forces thought to move tectonic plates.
• Explain how scientists measure the rate at which tectonic plates move.
Section 3 The Theory of Plate Tectonics
Chapter 15
Tectonic Plate Boundaries• As scientists’ understanding of mid-ocean ridges and magnetic reversals grew, a theory was formed to explain how tectonic plates move.
• Plate tectonics is the theory that explains how large pieces of the Earth’s outermost layer, called tectonic plates, move and change shape.
Section 3 The Theory of Plate Tectonics
Chapter 15
Tectonic Plate Boundaries, continued• A boundary is a place where tectonic plates touch.
•All tectonic plates share boundaries with other tectonic plates.
• The type of boundary depends on which direction the tectonic plates move.
Section 3 The Theory of Plate Tectonics
Chapter 15
Tectonic Plate Boundaries, continuedThree types of boundaries:
Convergent BoundariesDivergent BoundariesTransform Boundaries
Section 3 The Theory of Plate Tectonics
Chapter 15
Tectonic Plate Boundaries, continued•Convergent boundary – the boundary formed by the collision of two lithospheric plates.
• What happens at convergent boundaries depends on the kind of crust at the leading edge of each tectonic plate.
Section 3 The Theory of Plate Tectonics
Chapter 15 Section 3 The Theory of Plate Tectonics
Chapter 15
•Divergent boundary – the boundary between two tectonic plates that are moving away from each other.
• New sea floor forms at divergent boundaries. Sea-Floor Spreading.
Tectonic Plate Boundaries, continued
Section 3 The Theory of Plate Tectonics
Chapter 15
• Transform boundary – the boundary between tectonic plates that are sliding past each other horizontally.
• The San Andreas Fault in California is an example of a transform boundary.
Tectonic Plate Boundaries, continued
Section 3 The Theory of Plate Tectonics
Chapter 15 Section 3 The Theory of Plate Tectonics
Chapter 15
Causes of Plate Movement
• What causes the motion of tectonic plates?
•Tectonic plates move because of changes in the density in the asthenosphere.
• The following Visual Concept presentation examines three possible driving forces of tectonic plate motion.
Section 3 The Theory of Plate Tectonics
Chapter 15
Tracking Plate Movement• Tectonic plate movements are so slow and gradual that you can’t see or feel them.
•Tectonic plate movement is measured in centimeters per year.
• Scientists use a system of satellites called the global positioning system (GPS) to measure the rate of tectonic plate movement.
Section 3 The Theory of Plate Tectonics
